Activation of Progesterone Receptor by ATP

Progesterone-receptor complex from freshly prepared hen oviduct cytosol acquired the ability to bind to
isolated nuclei, DNA-cellulose and ATP-Sepharose when incubated with 5-10 mM ATP at 4°C. The extent of
this ATP-dependent activation was higher when compared with heat-activation achieved by warming the progesterone-
receptor complex at 23 °C. The transformation of progesterone-receptor complex which occurred in a
time-dependent manner was only partially dependent on hormone presence. The ATP effect was selective in
causing this transformation whereas ADP, AMP and cAMP failed to show any such effect. The non-hydrolizable
analogs of ATP, adenosine 5'-[a,/3-methylene]triphosphate and adenosine 5-[/l,y-imido]triphosphate were also
found to be ineffective. Presence of 10 mM sodium molybdate blocked both the ATP and the heat-activation of
progesterone-receptor complex. Mn" or Mg` had no detectable effect on the receptor activation but the presence
of Ca" increased the extent of ATP-activation slightly. EDTA presence (> 5 mM) decreased the extent of
receptor activation by about 40 % and was, therefore, not included in the buffers used for activation studies.
Divalent cations were also ineffective when tested in the presence of 1- 5 mM EDTA. The
properties of progesterone-receptor complex remained intact under the above conditions when analyzed for
steroid-binding specificity and Scatchard analysis. However, the ATP-activated progesterone-receptor complex
lost the ability to aggregate when tested on low-salt sucrose gradients. ATP was equally effective in activating
the rat-uterine estradiol-receptor complex at 4 "C and influenced the transformation of 4-S receptor form into
a 5-S form when analyzed on sucrose gradients containing 0.3 M KCI. The presence of ATP also increased the
rate of activation of progesterone-receptor complex at 23 °C. These findings suggest a role for ATP in receptor
function and offer a convenient method of studying the process of receptor activation at low temperature and
mild assay conditions.